1. Field of the Invention
The present invention relates to a tire pressure monitoring system that measures vehicle tire pressures and notifies an occupant of the resulting status.
2. Description of the Related Art
To aid in vehicle running safety, a tire pressure monitoring system (TPMS: The Pressure Monitoring System) is known which measures tire pressures of the vehicle to allow the pressure status to be indicated to an occupant of the vehicle. With the tire pressure monitoring system of this kind, it is desired for a vehicle occupant to be reliably notified of the tire pressure status in the occurrence of an abnormality in tire pressure and conserve power consumption. Various proposals have heretofore been made in the past to provide technologies such as those disclosed in Japanese Patent Provisional Publication No. 9-175124.
Technology disclosed in Japanese Patent Provisional Publication No. 9-175124 contemplates to set a low power consumption mode in a normal state to allow signals to be transferred or received at given time intervals for checking a system. When an abnormality occurs in the tire pressure, the low power consumption mode is cancelled so as to enable a signal indicative of the abnormal tire pressure to be transmitted or received and notify a vehicle occupant. This notification provides a capability of rapidly and reliably notifying the occupant of an abnormality in tire pressure while suppressing power consumption to a minimal during a period when no abnormal tire pressure occurs in tire pressure.
However, the technology mentioned above is premised on a fact that when an abnormality in air pressure is detected and a signal indicative of the abnormality is transmitted, a receiver circuit mounted on-board the vehicle for receiving the resulting signal remains in an operative condition. Such a system is effective for a running (moving) vehicle which is adapted to supply electric power to the receiver circuit at all times. In contrast, considering that the receiver circuit is turned off during, for instance, parking of the vehicle, the receiver circuit on-board the vehicle is disenabled and cannot receive the resulting signal even when the resulting signal, indicative of an abnormal tire pressure, is rapidly transmitted from the relevant tire, resulting in useless operation in transmitting the resulting signal from the abnormally inflated/deflated tire.